A new model for the global patterning of spores and pollen grains.

Spores of fungi and seedless plants, and pollen grains of seed plants, are usually characterized by variable global patterns on the surface. However, the mechanisms responsible for the development of these patterns have not been fully understood. We hypothesize that the global pattern of a spore or pollen grain is induced by the stresses resulted from the mismatch between a faster-growing outer part and a slower-growing inner part within the grain and tried to verify the hypothesis by simplifying the developing spores and pollen grains as stressed core/shell structures, simulating the buckling patterns of such structures with different shapes and shell thicknesses through finite element method, and comparing the simulated models with natural spores and pollen grains observed under microscopes. Totally, 313 models were simulated and 77 natural instances were studied. The simulated models reproduced various global patterns generally corresponding to the natural instances from a mechanical point of view. Our findings suggest that stress-driven development potentially contributes to the global patterning of spores and pollen grains, with the shape and thickness of the faster-growing outer part at the beginning of the differential growth determining the pattern types, providing new insights into the development and evolution of the global patterns on spores and pollen grains.